This invention relates to apparatus for providing radiant energy to enhance and test plant growth, and more particularly to apparatus that uses optoelectronic devices such as light emitting diodes to provide such radiant energy.
Several types of devices are known for providing radiant energy to enhance and test plant growth. Typical prior art electrical light sources include fluorescent, high pressure sodium, and other metal halide lamps. These prior art devices have several major disadvantages.
One disadvantage of metal halide lamps is that they provide a great deal of infrared and/or heat energy. Excessive infrared and heat energy has a deleterious effect on plants. To overcome this disadvantage, typical prior art devices must be placed at a sufficient distance from the plant to prevent plant damage. When the device is being used with a leaf chamber to test the ability of the plant to transform the radiant energy into chemical energy, extensive additional apparatus is required to remove the infrared and heat energy to prevent harm to the leaf. The use of such additional cooling and ventilating apparatus greatly increases the effective cost of the radiant energy.
Another disadvantage of metal halide energy sources is that the light intensity cannot be continuously reduced to a zero intensity since metal halide lamps require a minimum voltage to maintain the arc in the lamp. Since it is often desirable to reduce the energy output to a zero or a near zero intensity, the metal halide lamps are not suitable for some applications.
Typical prior art metal halide and other electrical energy sources output light having a relatively broad spectrum. However, it has been found that plant growth does not require the full spectrum of visible light. Thus, it is desirable to provide radiant energy sources that emit radiation in one or more specific regions of the spectrum.
U.S. Pat. No. 5,012,609 issued May 7, 1991 to Ignatius et al discloses an array of light emitting diodes which provide radiant energy in specific regions of the spectrum. However, a light emitting diode array like that disclosed in U.S. Pat. No. 5,012,609 requires a plurality of discrete light emitting diodes that must be plugged into a circuit. That arrangement limits the number of light emitting diodes that may be packed into the array. It is also somewhat expensive to manufacture and assemble an array of light emitting diodes using discrete components. Also, the power requirements for such arrays, as well as for metal halide lamps, are relatively large, increasing the cost of operation of the electrical energy sources.